Linear motion guide units have been extensively incorporated in recent years between relatively sliding parts in increased industrial fields including machine tools, various assembling machines, conveyors, and so on. Most prior linear motion guide units have been ordinarily fed with lubricant every a preselected interval based on maintenance schedules to make certain of forming the lubricant film separating the rolling elements from the circulating race, ensuring continuous smooth rolling motion of the rolling elements throughout a circulating circuit. Recently advanced machines and instruments, nevertheless, are increasingly needed to make them virtually maintenance-free from many aspects of conserving energy as well as keeping running cost and maintenance cost of equipment reasonable. Correspondingly, the linear motion guide units incorporated in the advanced machinery, especially the linear motion guide units of the sort of roller bearings are also challenged to keep the consumption of lubricant to a minimum, along with keeping linear motion guide units virtually maintenance free for long-lasting lubrication. Most conventional linear motion guide units are composed of an elongated guide rail and a slider that moves relatively to the guide rail by virtue of more than one rolling element, which is allowed to roll through a recirculating circuit that is made up of a load-carrying race defined between the guide rail and the slider, and a non-loaded area including a return passage and forward and aft turnaround passages made in the slider. With the linear motion guide units constructed as stated earlier, continuous application of lubricant on or between the load-carrying race and the rolling element is inevitable to continue maintaining an adequate lubricant film between the load-carrying race and the rolling element to keep them against metal-to-metal contact that might otherwise occur, thereby making sure of their high durability.
In the commonly assigned Japanese Patent Laid-Open No. H11-93952, there is disclosed a linear motion guide unit in which a lubricant applicator is provided with lubricating plates that are so constructed as to make their handling work including attachment and/or detachment from the guide rail easier. The lubricant applicator built in the prior linear motion guide unit is composed of a casing secured on an outward end surface of an end cap and lubricating plates made of sintered resinous members of porous or cellular texture whose interstices are filled with lubricant. The lubricating plates are harbored in the casing in a geometric relation that their raised tips are urged directly against raceway grooves on a guide rail to come into sliding engagement with the raceway grooves, keeping continuing lubricant application to the raceway grooves. With the prior linear motion guide unit whose lubricating plates constantly comes into sliding engagement with their associated raceway grooves, a major problem would raise that the sliding friction due to the engagement of the lubricating plates with the raceway grooves causes much sliding resistance acting on the slider. As a result, it will be understood that the linear motion guide units with the lubricating plate constructed as cited above are unfit for the machines or apparatus to be operated at high speed, where the linear motion guide units incorporated is needed to drive their sliders with high traveling speed.
Another Japanese Patent Laid-Open No. H11-22726 discloses a linear motion guide unit in which a slider having a movable body including a table, and so on thereon is allowed to move along a guide rail as more than one ball or roller built in the slider rolls through a circulating circuit. With the prior linear motion guide unit recited earlier, end seals adapted to be secured to forward and aft ends of the slider are each provided therein with a lubricant port and a lubricant groove communicating with the lubricant port while made open to a turnaround passage. The lubricant groove is rimmed evenly with raised edges to prevent the lubricant from leaking out through between the mating surfaces of the end seal and the associated end of the slider.
A further another linear motion guide means operational with less lubricant supply is disclosed in Japanese Utility Motel Laid-Open No. H05-71443, which is envisaged delaying the time interval for lubricant supply into a bath, thereby reducing the lubricant supply cycles to simplify lubricant supply operation with accompanying reduced maintenance for lubrication. With the prior linear motion guide unit recited earlier, enclosed lubricant reservoirs fit into their associated recesses cut in the outward surfaces of the forward and aft end caps. The lubricant reservoirs are made to communicate with the turnaround passages of the ball circulating circuit. The lubricant reservoirs are made integrally with spouts that are made to lead the lubricant out of the reservoirs into their mating lubricant paths made open to the turnaround passages. The lubricant enough in amount to prevent scuffing and wear in the ball circulating circuit may reach the turnaround passages through the combined spouts and lubricant paths. With the prior linear motion guide unit constructed as stated earlier, thus, the lubricant reservoir to hold the lubricant therein is needed, and the spouts of the reservoir have to be placed as close as possible to the turnaround passages to make sure of smooth flow of the lubricant out of the lubricant reservoir.
Another commonly assigned Japanese Patent Laid-Open No. 2006-105310 discloses a linear motion guide unit usually classified as a roller type using rollers as the rolling elements, which can work for long-lasting service life with accompanying substantive maintenance-free for lubrication. With the linear motion guide unit recited here, the return passage is constituted with a tubular composition made up of a tubular skeleton made therein with window, and a cellular molded member that fits into the window in the tubular skeleton. The tubular composition to provide the return passage in the prior linear motion guide unit is high in mechanical stiffness and also suited to provide steady application of lubricant around the rolling elements rolling through the return passage, ensuring positive lubrication over a long-term operation with reduced maintenance or maintenance-free. However, the tubular composition constructed as stated earlier is too sophisticated for production. The return passage is defined inside a hole of the tubular composition installed in a fore-and-aft bore made in a carriage of a slider. The tubular composition is composed of the tubular skeleton made therein with windows, and the cellular molded members that fit in the windows. The rolling elements of cylindrical roller, when coming into rolling-contact with the cellular members while rolling through the return passage, are applied with lubricant film. There, it remains a major challenge to develop any linear motion guide unit that is capable of reserving ample quantity of lubricant irrespective of more simplified in construction than the prior art as stated earlier.
Meanwhile, there are two members of the class of linear motion guide units, one of which has balls and the other has cylindrical rollers. With the linear motion guide unit in which cylindrical rollers are selected as the rolling elements, alignment problems to guide rollers in good rolling order without leaning in rolling posture are more encountered, compared with the construction using balls. To cope with this, the cylindrical rollers have to be guided not only on their circular rolling surfaces, but also on their axially opposite end surfaces. Conventionally, there is no linear motion guide unit constructed to meet with an aspect of allowing the rollers to roll through the circulating circuit over a long-lasting service life with adequate application of lubricant, making certain of steady reliability of the maintenance-free on lubricant application. Advanced technology has come to hope a linear motion guide unit which, even though simple in construction in favor of commercial production, is capable of retaining ample lubricant enough to make sure of steady and sustainable lubrication over a long-lasting service life for the cylindrical rollers that roll through a circulating circuit.